Rapid advances in fiber optics and VLSI technologies have made intelligent, high-speed telecommunication transport systems increasingly available to network providers. In such high-speed optical fiber networks carrying, for example, multiple gigabits per second of information, the failure of a key carrier link can result in an enormous loss of bandwidth and correspondingly great loss of service to users. Consequently, automatic network restoration is one of the most essential elements in the effective operation of these telecommunicatin networks.
A number of restoration systems have previously been proposed, but none has the capability of providing the economies of both time and facilities that are required in the expanding telecommunication fiber networks. For example, while the technique of diversely routed automatic protection switching can provide substantially complete recovery with a response time of about 50 milliseconds, the required redundancy of dedicated bandwidth results in a most inefficient utilization of equipment and network facilities. Somewhat more effective systems have been made possible, however, as highly intelligent digital cross-connect equipment is being broadly deployed throughout the networks, yet these generally are lacking in speed or are excessively complex.
One such recovery system which relies upon centralized management to reconfigure a network around a failure is described by Hasegawa et al. in "Dynamic Reconfiguration of Digital Cross-Connect Systems with Network Control and Management," Proc. of Global Communications Conference, November 1987. While such a centralized method can recover from individual logical switch problems as well as physical link failures, the extensive communication necessary between the control and operating elements of the system taxes available facilities and extends response time to as much as thirty minutes. On the other hand, a distributed recovery method, such as discussed by Grover in "The Selfhealing Network: A Fast Distributed Restoration Technique for Networks Using Digital Cross-Connect Machines," Proc. of Global Communication Conference, November 1987, with its inherent parallel processing achieves significantly higher response times, yet it suffers from message overloading due to the uncontrolled "flooding" (see Stallings, "Data and Computer Communications," Macmillan, 1985, pp. 256-261) employed in intrasystem message propagation.
Unlike these prior systems, the present invention utilizes a method of selective message propagation among digital cross-connect devices to yield a distributed control technique that provides an effective network restoration system having a degree of rapid response time and minimal communication congestion not previously available.